Credit Quality - Recorded Investment in Impaired Loans and Related Allowance by Class (Parenthetical) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 1,487	$ 1,382
Commercial Portfolio Segment | TDR on accrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	34	60
Commercial Portfolio Segment | TDR on nonaccrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	235	147
Residential Mortgage Loans | TDR on accrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	748	724
Residential Mortgage Loans | TDR on nonaccrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	10	12
Consumer Portfolio Segment | TDR on accrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	210	237
Consumer Portfolio Segment | TDR on nonaccrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 45	$ 41